RH Wiki:BPM
This policy provides information regarding listing a game's BPM in its infobox.
What is BPM?
A song's tempo is essentially how fast the song plays, measured in beats per minute. In the Rhythm Heaven Series, every game naturally needs a tempo to dictate how fast it plays, both the music and the gameplay accompanying it. This is not something the games ever explicitly show to the player, instead letting them get into the groove on their own. Rhythm Heaven Wiki has long had difficulty in finding how to best convey this information, with multiple factors (listed below) leading to the decision to simply not show it at all. Despite this, many attempts have been made to have it displayed anyway. As such, this policy intends to explain the reasoning behind this decision.
Why does the infobox not show it?
As mentioned above, this information is not explicitly shown during gameplay. As such, it would have to be discovered through datamining the games, or otherwise externally measured. In a lot of cases, this would just be a single number which shows how many beats per minute the music is. This gets complicated however when one has to consider the following points:
Tempo Changes
Some games change the tempo in the middle of the game. This may be simple for games such as Tap Trial or Power Calligraphy, which change the tempo only a handful of times throughout the song, but some games such as See-Saw or Iai Giri change the tempo very often. Displaying each and every tempo the song reaches would be comprehensive, but would quickly bloat the infobox. Extrapolating only a few BPMs (such as the base tempo, fastest and slowest) would alleviate that problem, but it would lead to incomplete information. This point also counts for games whose tempo was changed in later appearances, such as Quiz Show being slowed down from ~138 BPM in Rhythm Tengoku to 120 BPM in Rhythm Heaven Megamix, as well as any differences during Practice, in the Studio, Music Corner or Soundtracks. Many Endless Games change the tempo over time as a means of raising the difficulty, which opens the question of should every tempo change in these games be documented as well.
Refresh Rates
Due to the refresh rate of the Game Boy Advance and Nintendo DS families of systems not being an exact 60 FPS, the tempo for sequenced music in games played on these systems is effectively slower than what the internal value suggests it should be. For example, a game in Rhythm Tengoku set to 120 BPM internally would actually play closer to 119,455001139212 BPM on original hardware due to this. This discrepancy would mean the objective, internal value would be inaccurate to what actually happens during gameplay, and as Rhythm Tengoku can be played on multiple models and consoles, through emulators, and an arcade port, each with their own differences in refresh rates, what the exact effective tempo would be can vary quite a bit. The same holds true for sequenced music in later games to potentially lesser extents.
Streamed music does not provide a completely objective number either, due to being stored as the duration of the song in beats and duration in seconds divided by the sample rate. This creates tiny inaccuracies in tempo, for example Karate Man Combos! is set to 402 beats and 4 287 988/32 000=133,999625 seconds. Diving the beats by the seconds and multiplying by 60 FPS, we get 180,000503732753 BPM. This can be reasonably rounded to 180 BPM, with the decimal difference being negligible, though the exact decimal can also be unclear.
Objective Values VS Subjective Measuring
Some games may "feel" as a different tempo to what the game considers it to be. For example, Rap Men is, disregarding refresh rates, internally 180 BPM, but "feels" like 90 BPM during gameplay. This has led to disagreements over whether the number should be the more objective internal value, or the more subjective one. The difficulty in finding an objective number, and subjective measuring being prone to errors, would also mean that Rhythm Heaven Wiki would be including potentially incorrect information.
Conclusion
Being that this information is not shown to the player, and as such is not necessary to play the game, this puts into question what benefit there would be to showing it on the infobox. So far, no such agreed upon solution has been found for BPMs.